1. Technical Field
This invention relates to the technology of rapidly cutting low thermal conductivity materials such as foams, plastics, and fabrics, and more particularly to the technology of using fluidized jets to remove or sever surface discontinuities.
2. Discussion of the Prior Art
Conventional methods of removing surface discontinuity, such as edge salvage from plastics or foam bodies used in seating material for automobiles, has comprised either the manual use of razor sharp knives or use of heated wires as a hybrid mechanical and thermal process. Each of these methods is intensive in labor requirements, and thus high in cost, and lacks accuracy in cutting or severing because of manual guidance.
Similarly, sand or grit blasting has been carried out for years to remove surface discontinuities; this is a mechanical impact process. The particles may include a variety of solid materials such as sand, glass beads, walnut shells, and may include nonsolids such as steam and chemical solvents. The problem with this straight mechanical approach is that it not only removes discontinuities, but it also abrades desirable parts of the workpiece itself and cannot achieve clean-cut straight edges.
Water jets have recently been used to cut soft materials; this again is a straight mechanical process that uses the high pressure of a dense liquid, at room temperature, to carry out the severing. The problem with a water jet is that it also provides an imprecise edge cut, often a ragged fracture, and is unable to cut through many types of low thermal conductivity workpieces.
A modern approach to removing surface discontinuities is disclosed in U.S. Pat. No. 3,676,963, which attempts to clean burrs or other flashing from a metallic or plastic workpiece by using the mechanical impact of solid ice particles sprayed thereagainst without convergence. The kinetic energy of the solid ice particles fractures the burrs by repeated impact which exceed the bending fatigue limit of the burrs. This mechanical impact process is assisted by the high density of the ice particles in the range of 0.89-0.98 g/cm.sup.3 and by the cooling effect of the ice particles. The particles must be sized relatively large, such as 16-20 mesh, and conveyed in a fluidized stream of liquid nitrogen or air. Unfortunately, the particles, being relatively large and sprayed in a nonconverging pattern, do not cut straight edges but instead fracture fragments of the workpiece by kinetic energy. The ice particles are sprayed from a straight nozzle having identical inlet and outlet diameters or by use of an aspirator nozzle having a venturi throat; each nozzle employs a small orifice concentric with the nozzle throat to promote expansion and therefore the spraying effect.
The principal goal of this invention is to provide a method of robotically cutting low thermal conductivity materials that are not subject to removal by frangible bending fatigue.